Both in vitro and in vivo experimental studies proved that insulin has an important anabolic role. This physiological function of insulin is reflected in its well documented involvement in protein metabolism and in acceleration of cell proliferation. Support for a growth promoting action of insulin is further provided by clinical studies that revealed that children with hypoinsulinemia have a decreased growth rate whereas, on the other hand, children with hyperinsulinemia have an accelerated growth. While it was initially assumed that the growth activities of insulin are facilitated via cross-talk with the closely related insulin-like growth factor-1 receptor (IGF-1R), it is now clear that the vast majority of these activities are mediated via direct interaction with the insulin receptor (IR). The present article provides an overview of the growth and proliferative actions of insulin, with an emphasis on a number of pathological conditions, including cancer.